The present invention relates to a semiconductor device of high blocking capability including a semiconductor body having at least two differently doped layer-type zones of alternatingly opposite conductivity type with a pn junction therebetween, the jacket or edge surface of the semiconductor body enclosing, in its path from the higher doped zone to the lower doped zone, in the region where the pn junction exits, an angle of less than 90.degree. with the pn junction surface.
When semiconductor rectifiers are used, undue excess voltages at the pn junction can produce a so-called field strength breakthrough on the surface of the preferably wafer-shaped semiconductor body which can lead to destruction of the semiconductor device. In order to prevent such an occurrence, and to limit the undue excess voltages by a reversible so-called field strength breakthrough in the volume, it is known to form the semiconductor body with a frustoconical shape by slanting or sloping the edge surface in the vicinity of the pn junction. In this case the normal to the pn junction surface disposed in the region of the exit of the pn junction at the jacket or edge surface of the semiconductor body and pointing in the direction of the lower doped zone forming the pn junction, which lower doped zone lies between higher doped zones, encloses an angle of less than 90.degree. with the normal to the semiconductor body jacket surface at least in the regions over which the barrier layer of the associated pn junction extends.
In view of such a configuration the constant voltage areas extending in the lower doped zone parallel to the pn junction surface have a greater mutual distance in the vicinity of the jacket surface than in the interior of the semiconductor body. Such a configuration is known as a so-called positive slant or slope. A negative slant or slope is given if in the corresponding region the normal to the pn junction surface extending in the direction of the lower doped zone forms an angle greater than 90.degree. with the normal to the jacket surface.
With the appropriate polarization of the voltage across the semiconductor body a positive slant produces a widening of the space charge zone at the jacket surface while a negative slant leads to a constriction or narrowing of the space charge zone and thus to a reduction in the critical surface field intensity.
Semiconductor arrangements are known whose semiconductor bodies are provided with a negative slant in the jacket surface in order to produce a higher blocking capability.
FIG. 1 is a partial sectional view of such a known layer sequence with one pn junction for a rectifier diode. The semiconductor body of the embodiment of FIG. 1 includes a weakly doped center zone 1 of n-type conductivity, a higher doped outer zone 2 of p-type conductivity which forms the pn junction S with zone 1 and an outer zone 3 of n-type conductivity which is opposite p-conductive zone 2. This type of configuration, forming a so-called psn layer sequence, is also provided with electrodes 12 and 13 on the outer surfaces of zones 2 and 3 respectively and is provided, in a known manner, with slanting or sloping jacket surfaces indicated by the reference numberal 11. With the appropriate polarity of the voltage applied thereto the illustrated formation of areas with constant voltage results, particularly in the center zone 1.
It is also known, in a semiconductor body having at least three zones of alternatingly opposite conductivity type, as is the case in thyristors, to provide a positive slant extending to the lower doped center zone in the region of one of the pn junctions and then, beginning in the center zone, to provide an identically directed but substantially less steep further slant in the region of the other pn junction. The second slant is negative but, in view of the very acute angle of preferably 6.degree. to 8.degree. it also results in an expansion of the space charge zone at the jacket surface.
FIG. 2 is a partial sectional view of such a known layer sequence with two pn junctions for a thyristor. The layer sequence shown in FIG. 2 with three zones of alternatingly opposite conductivity type is provided with pn junction S.sub.1 and S.sub.2 between the high-ohmic n-type conductivity center zone 1 and the two p-type conductivity zones 2 and 4, respectively, which are adjacent each side of the zone 1. The first pn junction S.sub.1 opens into the positively slanted region 11, while pn junction S.sub.2 opens into the negatively slanted region 21 which begins in the center zone 1.
An extreme drawback of both of these known arrangements is the considerable loss of active area, i.e. the area serving to conduct current through the semiconductor body, particularly in the case of a semiconductor body with a double slant, a so-called double faceting, as shown in FIG. 2. Moreover, the production of the so-called double-faceted design for semiconductor bodies intended for thyristors involves considerable production costs.